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Abstract

A combination of several searches for Standard Model Higgs boson production
at CDF using a data sample up to 3.6 fb-1 of integrated luminosity
is performed. The channels considered are WH-> lνbb,
VH->METbb,
ZH->l-l+bb,
gg -> H -> W+W-, and a search H->&tau-&tau++2jets.
We calculate combined upper limits on the ratio of
the Higgs boson cross section times the branching ratio to its Standard Model prediction(R95) for
Higgs boson masses between 100 and 200 GeV/c2.
The results are in good agreement with the expectations obtained from background-only
pseudo-experiments. The 95% CL upper limits observed (expected) are
factors of 3.64 (3.22) and 1.42 (1.59) higher than the Standard
Model production cross sections for Higgs boson masses of 115 and
160 GeV/c2, respectively.

Cross Sections

The cross sections at points not specified in the TeV4LHC Tables are obtained
by interpolating log(cross section) vs. mH between neighboring points in the table. These cross sections have been verified with
MCFM.

The gg -> H production cross section is calculated at NNLL in QCD
and also includes two-loop electroweak effects. For details, see
C. Anastasiou, R. Boughezal and F. Petriello, "Mixed QCD-electroweak
corrections to Higgs boson production in gluon fusion",
arXiv:0811.3458 [hep-ph] (2008). and D. de Florian and M. Grazzini,
"Higgs production through gluon fusion: updated cross sections at
the Tevatron and the LHC", arXiv:0901.2427v1 [hep-ph] (2009).

The combined upper limit as a function of the Higgs boson mass between 100 and 200 GeV/c2.
Solid lines indicate the observed upper limit for each channel and
combined result (dark red). Dashed lines indicate the median expected upper limit for each channel and the combined result (dark red).

The summary table of observed and expected limits between 100 and 200 GeV/c2.

Posterior Probability

Posterior densities for all channels combined for Higgs boson mass between 100 and 200 GeV/c2.

Expected Limits with Pseudo-experiments

Limits are computed with simulated data sets drawn from systematically varied template histograms.
The observed limits are indicated with red vertical lines. The median expected limits in the absence of a Higgs boson signal
are shown with dashed vertical lines. 68% of limits are expected to fall within the green shaded area, and 95% of limits are expected
to fall within the top and bottom of the yellow-shaded areas, again assuming no signal is truly present.

Events Ranked by s/b

Events in all search channels, sorted by the s/b in the bins in which they are found. Signal and background totals are shown, not stacked.
This plot is shown for mH=115 GeV/c2

Cumulative distributions of background, data and signal+background. The s/b distribution is integrated from the high s/b side downwards.
This plot is shown for mH=115 GeV/c2

Events in all search channels, sorted by the s/b in the bins in which they are found. Signal and background totals are shown, not stacked.
This plot is shown for mH=160 GeV/c2

Cumulative distributions of background, data and signal+background. The s/b distribution is integrated from the high s/b side downwards.
This plot is shown for mH=160 GeV/c2

Projections

Achieved and projected median expected upper limits on the SM Higgs boson cross section, by date. The solid lines are 1/sqrt(L)
projections. The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom
of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25.
The bottom plot is the same as the
top plot but has a logarithmic scale for the expected limit.
These plots are shown for mH=115 GeV/c2

Achieved and projected median expected upper limits on the SM Higgs boson cross section, by date. The solid lines are 1/sqrt(L)
projections. The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom
of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25.
The bottom plot is the same as the
top plot but has a logarithmic scale for the expected limit.
These plots are shown for mH=160 GeV/c2

2xCDF Projections

Projected median expected upper limits on the SM Higgs boson cross section, scaling CDF performance to twice the luminosity.
The solid lines are 1/sqrt(L) projections, as functions of integrated luminosity per experiment.
The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom
of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25.
This plot is shown for mH=115 GeV/c2

Projected median expected upper limits on the SM Higgs boson cross section, scaling CDF performance to twice the luminosity.
The solid lines are 1/sqrt(L) projections, as functions of integrated luminosity per experiment.
The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom
of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25.
This plot is shown for mH=160 GeV/c2

Probability of seeing a 2σ excess as a function of mH for analyzed integrated luminosities of 5 fb-1 and
10 fb-1 per experiment, assuming CDF and D0 perform the same. Two scenarios are shown, in which channels have the same performance
as for the current combination (Winter 2009, solid lines), and for the case with another factor of 1.5 in the sensitivity (dashed lines).
The current observations are not taken into account, only expected sensitivities are shown. Sensitivities are expected to scale with sqrt(L).

Probability of seeing a 3σ excess as a function of mH for analyzed integrated luminosities of 5 fb-1 and
10 fb-1 per experiment, assuming CDF and D0 perform the same. Two scenarios are shown, in which channels have the same performance
as for the current combination (Winter 2009, solid lines), and for the case with another factor of 1.5 in the sensitivity (dashed lines).
The current observations are not taken into account, only expected sensitivities are shown. Sensitivities are expected to scale with sqrt(L).

Experimental Contacts

If you wish
to present this material publicly or would like further information,
please email the CDF combination group and conveners